1. Field of the Invention
The present invention concerns an image system for processing image data in the form of grey-scale value signals and generating of an image that can be displayed on a presentation device, in particular for a medical diagnostic device, of the type having a circuit to harmonize the image data.
2. Description of the Prior Art
Image systems of the above type are known and are used primarily in connection with x-ray diagnostic devices, wherein they serve to generate a diagnostically meaningful x-ray image using the image data acquired via the x-ray examination. Such x-ray diagnostic devices have an image converter to convert the x-ray image into an electrical analog signal sequence, an image or, a video signal. Such an image converter can be, for example, a solid-state image detector. Since medical image systems generally are fashioned digitally, the supplied image signals are converted into corresponding digital values, for which the x-ray image is separated into different image points (pixels) with which different digital grey values are respectively associated. The acquired images normally are presented to the physician on a suitable monitor as grey-scale images for assessment of the diagnosis findings.
Furthermore, it is known to process the acquired image data or the grey-scale value signals in order to specifically change the generated image with regard to the image impression or effect, in order to be able to extract different information from the generated image. One such image processing technique is known as harmonization, also known as DDO (Dynamic Density Optimization). In such harmonization, frequently also called Dynamic Range Control or “dynamic compensation” or “dynamic balancing,” the originally acquired image data, known as “raw image data”, are filtered with a weighted low-frequency filter, undergoing a smoothing of the image data. A shrinking of the grey-scale value range in which the image data lie ensues by this low-frequency filtering, i.e. the image overall becomes “flatter”, the contrast decreases. Although the high-pass filtering causes the higher-frequency portions to be advantageously filtered, the flattening of the image and decrease of the grey-scale value range and the contrast loss associated therewith lead to a changed image impression.
In order to be able to again compensate the “image flattening” that ensues via the harmonization, it is conventional for optimization actions to be manually applied by the physician or technician. Such actions in turn cause other image-determining parameters to be manipulated due to the manual change, such that the image impression is again changed and significance is lost. For example, the image brightness can disadvantageously be affected, so the image can become too dark or too light, etc.